docs: def index_agreement(s, o):
      """
          index of agreement
          input:
          s: simulated
          o: observed
          output:
          ia: index of agreement
          """
      # s,o = filter_nan(s,o)
      ia = 1 - (np.sum((o-s)**2)) /\
               (np.sum((np.abs(s-np.mean(o))+np.abs(o-np.mean(o)))**2))
      return ia